The Fischer-Tropsch process is one of several processes involving the hydrogenation of carbon monoxide and is well-known for producing hydrocarbons and hydrocarbon fuels by contacting mixtures of carbon-monoxide/hydrogen, with generally an iron-based catalyst. The produced hydrocarbons usually contain a broad range of liquid paraffins and olefins of C.sub.5 -C.sub.20 carbon number, and under conditions of excess hydrogen, an especially valuable portion being the linear and branched paraffinic C.sub.6 -C.sub.11 fraction, the well-known "gasoline" fraction useful for internal combustion engines.
An extensive amount of work has been carried out in an effort to modify and improve the selectivity of the process in producing the gasoline fraction directly under efficient process conditions, containing C.sub.6 -C.sub.11 aromatic hydrocarbons, to improve the octane number. Particular process conditions which are highly desirable are high percent CO conversion, low methane make, high liquid hydrocarbon make, substantial aromatics produced in the C.sub.5 -C.sub.11 hydrocarbon fraction and a low wax make (i.e., C.sub.23+ hydrocarbons). However, carbon monoxide hydrogenation processes utilizing iron-based catalysts are not now successful in producing C.sub.6 -C.sub.11 gasoline fractions containing a significant quantity of C.sub.6 -C.sub.11 aromatic hydrocarbons under the above-described efficient process conditions.
A commercially practiced Fischer-Tropsch process uses mixtures of carbon monoxide/hydrogen that are contacted with a potassium-doped iron catalyst, as a fluid bed, at about 320.degree. C. to 330.degree. C. under pressure. The resulting liquid hydrocarbons generally comprise only about 5 weight percent aromatics and in addition, a significant quantity of wax formation occurs.
What is desired is a process which is more selective in producing C.sub.6 -C.sub.11 liquid hydrocarbons in which the yield of aromatics, particularly in the C.sub.6 -C.sub.11 liquid hydrocarbon portion, is selectively higher than 5 weight percent, being preferably about 10 weight percent or higher. Particularly desired is where the process can be conducted under very efficient conditions of high percent CO conversion, high liquid hydrocarbon make, significantly high C.sub.6 -C.sub.11 aromatics content, low methane make and low C.sub.23+ hydrocarbon wax make.